Below are some tips and tricks for laser cutting and 3d printing design. If you have any suggestion please let us know and we would be happy to add the tips to the list.

Coral Draw         Kerf        Thread Inserts


Coral Draw Etching Images

Just a note – this is a less-precise process than cutting geometry…

Select Import… from the File menu, and select your image file.

Click to place the image, and resize according to the desired output.

NOTE – if you’re etching into acrylic (or other materials that will turn lighter when etched) you may want to invert the colors in the image.

Select Print… from the File menu, pick the appropriate laser, and click the Properties… button.

Set the Pen Mode to RAST for Black and None for everything else (the software will automatically convert any images to grayscale). Note – any Black geometry that is not part of the image will also be cut at the settings below, and any geometry other than black will not be cut.

Change the speed to 33% (the max raster speed), the PPI to 1000 and set the power to a value between 10 and 30 percent, depending upon how dark you want your etching (15 works well for MDF, 20 is good for acrylic, but it depends upon what you want). Don’t forget to hit the Set button, then OK a couple times to send the job to the laser.


The Enemy: Laser Kerf

The laser will cut away material centered along the geometry that you define. The total width of material removed is the kerf, which is approximately 0.007″. To generate a moderate press fit between two pieces, you must take this kerf into account when designing the mating parts. The effect of this kerf can be visualized in the image to the right, where the dashed line represents the cut line, and the solid bodies are what would be left after cutting. If you were to try to assemble these together, there would be a significant amount of wiggle room (approx. 0.014 inches – enough for 3 or 4 sheets of paper).

Getting a Line-on-Line Fit

If we would like to generate a line-on-line fit between the parts (as shown in the image to the right), you would want to either enlarge the peg or shrink the notch, it really doesn’t matter which. Set the width of the peg to be equal to the width of the hole plus two times the kerf (0.014″).

Getting a decent press fit

With somewhere between 0.001 and 0.002 inches of dimensional overlap, you should be able to create a quality press fit between two parts, though this is highly dependent upon a number of factors, including the compliance of the members and the magnitude of the dimensions. In other words, we could express this as

peg = slot + 2 * kerf + overlap

For more compliant (softer) materials, you’ll want to increase the overlap. For instance, when trying to achieve a solid press-fit box joint with acrylic (which is relatively stiff), you may find 0.002″ to 0.004″ of overlap to work well, while with MDF, you may find an overlap of between 0.006″ and 0.012″ might be suitable.

And it’s always a good idea to do a quick test cut to see what the kerf actually is in the material you are using. Kerf and cutting performance are also quite dependent upon both the laser focus and the cleanliness of the lens, so it’s hard to give exact values for the overlap without doing some preliminary testing.


 

Threaded Inserts 

Threaded inserts are small metal fasteners that can be pressed into holes in 3d printed and laser cut parts. We currently offer four sizes: 4-40, 6-32, 10-32, 1/4-20. To use the inserts please follow the below direction:

  1. Select the size thread you would like and add the according size to your printed part.
     4-40:  0.157 in
     6-32: 0.2211 in
    10-32: 0.2905 in
    1/4-20: 0.3745 in
  2. Collect your inserts and locate the arbor press in GM lab.
  3. Place the 3d printed part on the flat of the press with the hole vertical to the hammer.
  4. Hold the thread above the hole and gentle press the hammer. Remove fingers once the insert can be self supported.
  5. Press the hammer down until the insert is flush with the part.

If you are unsure or would like assistance please ask RPL staff!